The long-term goal of our investigation is to understand how neural circuits in the prefrontal cortex support decision-making. Orbitofrontal cortex (OFC) is a key brain region for decision- making under uncertainty in humans and other animals. Our central hypothesis is that OFC represents confidence information and plays causal role in reporting decision confidence to other brain regions, thereby affecting behavior. To study this issue, we have developed quantitative psychophysical methods for rodents, adapted from human and primate work, which enables the behavioral readout of confidence in a well-controlled decision task. Briefly, in each trial the animal has to decide which of two odor components is in the majority. After moving to the corresponding choice port, the rat waits for a delayed reward that may or may not come. If it doesn't, the rat eventually leaves the port and initiates another trial. The duration rats are willing to wait for a reward can be thought of as a gamble on the outcome of the perceptual decision, and hence it provides a quantitative index for confidence. Thus in each trial there is a perceptual decision (left/right) and a post-decision confidence report (leaving decision). If OFC is causal in this leaving decision, neural activity should be predictive of how long a rat waits before leaving on a trial-by-trial basis (correlation) We will also test the necessity of OFC activity for this process using pharmacological inactivation. These results will be interpreted in a computational framework that links neural and behavioral data to decision confidence. Next we will test the hypothesis that identified subsets of OFC neurons projecting to distinct target areas carry different types of information and thus mediate distinct behavioral functions. Using retrograde viruses to deliver light-sensitive activators (ChR2) and suppressors (Halo), we will optically microstimulate or block a subset of OFC neurons defined not by spatial proximity but by projection target. In combination with electrophysiology we will identify the neural correlates of distinct projection neurons and determine whether they are necessary and sufficient for confidence reports on a trial-to-trial basis. Upon completion of these aims, we expect to establish the role of OFC in decision confidence and determine the neural circuits through which it exerts its actions. By recording from neurons belonging to different long-range projections we also expect to help explain the observed heterogeneity in OFC neural representations. Beyond these mechanistic studies, we hope to inform an improved framework for understanding how impairments in a single prefrontal brain area can lead to such a wide range of psychiatric disorders, including addiction, depression, anxiety, obsessive-compulsive disorder, schizophrenia, and autism.